Dipole antenna



Feb. 10, 1948.,

S A. SCHELKUNOFF DIPOLE ANTENNA Filed April 20, 1943 #0 u 771. [2/1 T/ON A PPA RA Tus FROM .SOURCEOF OSC/LLAT/O S REC.

ELECTRON STREAM lNl/ENTOR By S.A.SCHLKUNOF F A TTOPNE V Patented Fe... 10, 1948 UNITED STATES PATENT O F Fl C E ,TJ IPOLE ANTENNA Sergei A; Schelkuuofi, New York, N. Y assi nor te Bell Telephone Laboratories, Incorporated,

.New Y'o'rlnNrYg a corporation of New York ApplicationApril'm), 1943, Serial No. 483,725

'4 claims.

This invention relatesto'dip'ole antennas useful fortheradiation and reception o'r electromagnetic waves of "wavefl'ehgthl '0 centimeters "or less, particularly a dipole making use'of velocity modulation of'ah electron stream for the'direct transfer of energy from such a stream to a radiation field or vice versa.

Numerous expedients are known for using velocity modulationoffelectron streams in the radiation or'rec'eption of ultra=highfrequency energy but o far no device haste-en suggested for the direct interchanged such ener y between the radiation field and "the stream. Examples of known expe'dients are disclosed in United States Patents 2,190,515,}bruary "13, 1940, to W. C. Hahn, and"2 24"7,33'8, June 24,1941, to S. Raine to which reference may be inade 'for '2. description of the me'an'sror establishing; "an electron stream of which the velocity is to be modulated.

The present invention; however, has'for its object to provide means for: an immediate energy interchange, in either direction, between the antenna and the stream. The invention will be understocdifrom'the following description read with re'ferenceto the accompanying drawing, the single figure of which represents a dipole antenna according to the invention.

In thefigure an evacuated cylindrical glass tube I, of over all length equalto the wavelength of the radiationtobe-transmitted or re 'ceived, includes an electrongun G and :an electron collector'K connected externally of tube I to battery 2 which provides a potential difference of, say 500 volts between gun G and collector K. Details of gun G, of collector K, and of the electrical connections to battery 2 are omitted, these being set forth in the patent to Ramo above referred to.

Tube I is coated externally with a conducting two-part metallic layer 3 and 3' which encloses tube I completely except for intervals left for electrical connections to battery 2 and others later described and except further for a cylindrical gap defined by the planes AB and CD transverse to the axis of tube I. Conveniently, planes AB and CD are located I centimeter apart and symmetrically with respect to the transverse plane halving the length of tube I.

It will be seen that metallic coatings 3 and 3' constitute a dipole antenna adapted to receive or radiate, most efficiently in the plane at right angles to the length of tube I, radiations of 100- centimeter wave-length. Coatings 3 and 3 may, of course, be metallic layers deposited in any 2 well-known way ormay be more substantial inetallic. shells fabricated to enclosetube "I and prov-ided'with appropriate apertures for electrical connections. Tube I maybe external to the dipole elements, withonly obvious changes from the arrangementin the figure.

Consider a radiation field R advancing in the direction shown by the arrow. If the wavelength of this radiation is 100 centimeters, a-voltage loop will appear acros the gap between the respective ends Ahead 6D of the elements of the dipole antenna, Theelectrons in the stream passing through tube I willexperience velocity modulation under the influenceof this voltage loop andlas a. result willbecomebunched insuce cessiveigroups after passingthe gap;

lithe electrons bunched .in groups asdust described continue toward collector. K passing on their wayapair o'f-g'rids 4 andl, B'etWeentheSe grids an alternating. electromotive-forceofthe frequency of the received radiation isdeveloped byeleetrostatic induction fromthepassing elect tron bunches and this electromotivefforce may be applied by connectionsas shown to receiving amplifier 5 leading toany convenient formof utilization-apparatus.

Likewise the dipole described mayserveas a transmitting. antenna provided that from. any convenient source. electrical oscillations of the resonant frequency are impressed through trans mitting amplifier B on the pair of grids 1-, 1 Groupingof the electrons will in th-iswcase take place in the drift space between grids I, I and the gap AB-CD resulting in a voltage loop across this gap whereby energy is radiated from the dipole, again with a maximum in the plane at right angles to the axis of tube I.

In each case the described apparatus serves to effect the interchange of high frequency energy directly between the radiation field and the electron stream traversing tube I, without any intermediate detecting or transforming equipment being required.

As an illustration a radiation of IOO-centimeter wave-length has been considered. For this case suitable dimensions of the apparatus are as follows: Tube I is centimeters in length while metallic dipole elements 3 and 3 are each 49.5 centimeters long to enclose both ends of tube I and leave the central gap 1 centimeter in axial length. The axial spacing between grids 4 and 4' and that between grids I and I are each suitably 1 centimeter. The diameter of dipole elements 3 and 3' is suitably a small fraction of their length, say 4 centimeters. The distance s between the Electron drift time in cycles= or Where \=100 centimeters s=12 centimeters.

While the invention has been described with specific reference to the reception or radiation of electromagnetic waves of IOU-centimeter wavelength uniformly in a plane at right angles to the axis of the dipole antenna, those skilled in the art will need no particular instruction to adapt the invention to receive or radiate in other than this transverse plane and the numerical relations given enable the ready computation of apparatus dimensions for wave-lengths longer or shorter than that chosen for illustration. Moreover, other'forms of energy transfer means may replace the grid pairs 4, 4' and'l, 7' without departing from the spirit of the invention.

What is claimed is: v

1. The method of effecting the direct interchange of electrical energy between an electron stream, and an externally generated radiation field which comprises establishing an alternating voltage loop in said field, generating a stream of electrons having a desired velocity, directing said stream in a path substantially parallel to the voltage gradient in the region of said loop and producing modulation of the velocity of said electrons in passing said loop.

2. A dipole antenna comprising two longitudinally aligned tubular members each of a length substantially equal to one-half of a desired Wavelength, the members at their adjacent ends being separated by a short gap across which an electric field develops in consequence of excitation of the antenna at its natural resonance frequency, a cathode ray source within one of the members and a collector within the other member and externally connected electrically to the source whereby the cathode ray when passing the gap interacts with the electric field thereacross and energy transfer means within each of said tubular members adapted to be electrically connected to an external circuit.

3. Means for the reception of electromagnetic radiation including a dipole antenna exposed to said radiation, comprising two longitudinally aligned tubular members each of length substantially equal to one-half of a desired wave-length,

said members being separated at their adjacent ends by a short gap across which an electric field develops in consequence of the excitation of the antenna at its natural resonance frequency by said radiation, a cathode ray source within one of said members, a, collector of cathode rays with in the other of said members and externally electrically connected to said source whereby the cathode ray when passing said gap interacts with the electron field across said gap and energy transfer means within said other member adapted to be electrically connected to an external receiving circuit.

4. Means for .the radiation of electromagnetic energy including a dipole antenna comprising two longitudinally aligned tubular members each of length substantially equal to one-half of a desired wave-length, said members being separated at their adjacent ends by a short gap across which an electric field develops in consequence of the excitation of said antenna at its natural resonance frequency, a cathode ray source within one of said members, a collector of cathode rays within the other of said members and externally electrically connected to said source and means 'for exciting said antenna at its resonant frequency including means for effecting velocity modulation of said cathode rays prior to their passage across said gap.

SERGEI A. SCHELKUNOFF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,284,829 Ludi June 2, 1942 2,231,935 Hansen et a1 May 5, 1942 2,235,527 McArthur.. Mar. 18, 1941 2,263,248 Roberts Nov.,18, 1941 

